If you can log into your computer in safe mode, open control panel, then "users" then create a new user account/administrator profile.. Then restart the computer in normal mode, you will have to enter the user name and password for this account manually, Once you are logged in with that new administrator account, you can make changes to revert two settings that I recommended, that would effect user logon; one is via services re-enable "fast user switching", and the other in control panel, security center, change the way users log on/ enable use the "welcome screen"